The goal of the proposed project is to understand the protein composition of ribonucleoprotein complexes containing microRNA miR-29b. MicroRNAs are endogenous, small regulatory RNA molecules. Numerous recent studies have demonstrated that microRNAs are important regulators of gene expression and play crucial roles in a wide range of physiological processes and diseases including cardiovascular and renal diseases. The effect of microRNAs on target genes is mediated by interactions of microRNAs with proteins that, together, form microRNA-containing ribonucleoprotein complexes (miRNPs). Despite the crucial and wide-spread functional role of microRNAs, the number of protein components of miRNPs that have been characterized is surprisingly small. The understanding of proteins interacting with specific microRNAs is particularly lacking, despite the recognition that different microRNAs may act differently. The shortage of knowledge in this critical area significantly hampers in-depth understanding of how microRNAs act, how the action of microRNAs is regulated, and how microRNAs contribute to the regulation of physiology and disease. We propose to develop a new approach for identifying protein components of miRNPs specifically containing miR-29b, a microRNA that we have shown to be functionally important in the protection against hypertensive renal injury. Aim 1 will develop the approach, identify the protein components, and provide initial characterization of the newly identified proteins. Aim 2 will examine the functional significance of the newly identified proteins.